The invention relates to an aluminum-free magnesium alloy and to the use for producing extruded semi-finished products or components and metal sheets.
Magnesium alloys are lightweight construction materials that, compared to alloys of other metals, have a very low weight and are used where a low weight plays an important role, in particular in automotive engineering, in engine construction, and in aerospace engineering.
Offering very good strength properties and low specific weight, magnesium alloys are of great interest as metallic construction materials most notably for vehicle and aircraft construction.
A reduction in weight is needed especially in vehicle construction since additional elements are being installed, due to rising comfort and safety standards. Lightweight construction is also important for the design of energy-saving vehicles. In terms of processing magnesium materials, methods involving metal forming by way of extrusion, forging, rolling, stretch forming or deep drawing are gaining importance. These methods allow lightweight components to be produced, for which demand is growing especially in vehicle construction.
Alloys having advantageous mechanical properties, and more particularly having high tensile strength, are included in the related art.
A magnesium alloy is known from DE 806 055 which is characterized by a composition of 0.5 to 10% metals from the group of rare earths, the remainder being magnesium, with the proviso that the rare earths comprise at least 50%, and more preferably at least 75%, neodymium, and no more than 25% lanthanum and cerium, separately or together, and praseodymium, and small amounts of samarium and traces of the elements of the yttrium group as the remainder, to which is added one or more of the following elements: manganese, aluminum, calcium, thorium, mercury, beryllium, zinc, cadmium and zirconium.
A magnesium alloy containing 2 to 8% rare earth metals is known from DE 42 08 504 A1, wherein the rare earth metal consists of samarium.
Further known magnesium alloys having advantageous mechanical properties comprise alloys containing zinc and mixtures of rare earth metals that have a high content of cerium. Such an alloy contains approximately 4.5 wt. % zinc, and approximately 1.0 wt. % rare earths having a high content of cerium. These alloys can achieve good mechanical properties but they are difficult to cast, making it difficult to cast parts of satisfactory quality. Welding may meet with difficulty if complicated assembled parts are involved.
Magnesium alloys having higher contents of other metal components, such as aluminum and zinc, which solidify with a fine-grained structure, have considerably worse corrosion properties than pure magnesium or magnesium-manganese alloys.
A silicon-containing, corrosion-resistant magnesium alloy having a fine-grained solidification structure is known from DE 1 433 108 A1. Manganese, zinc, and titanium are added to the magnesium alloy, in addition to silicon, and aluminum, cadmium and silver are added as further alloying components.
Additional alloys containing manganese as well as further elements such as aluminum, copper, iron, nickel, calcium and the like, in addition to magnesium as the main component, are known from DE 199 15 276 A1, DE 196 38 764 A1, DE 679 156, DE 697 04 801 T2, and DE 44 46 898 A1, for example.
The known magnesium alloys have a wide variety of drawbacks.
U.S. Pat. No. 6,544,357 discloses a magnesium and aluminum alloy containing 0.1 or 0.2 wt. % up to 30 or 10 wt. % La, Ce, Pr, Nd, Sm, Ti, V, Cr, Mu, Zr, Nb, Mo, Hf, Ta, W, Al, Ga, Si, B, Be, Ge, and Sb, along with other elements. The range of alloys that could potentially be produced here is so broad and unmanageable that it is impossible for a person skilled in the art to arrive at the alloy that is claimed hereinafter.
In alloys containing magnesium-aluminum-zinc-manganese or magnesium-aluminum-manganese, the strength is reduced at higher temperatures.
The overall metal forming behavior, weldability, or corrosion resistance is degraded.
The cold workability of the most common magnesium alloys is limited due to the hexagonal crystal structure and low ductility. The majority of magnesium alloys exhibit brittle behavior at room temperature. In addition to high tensile strength, a ductile behavior is needed for certain metal forming processes to produce semi-finished products from magnesium alloys. Higher ductility allows improved metal forming and deformation behavior, as well as greater strength and toughness.
Many of the known magnesium alloys have drastically varying properties in the produced state.
A further disadvantage in the production of magnesium alloys is that metallic manganese in the magnesium melt is poorly soluble or requires a long time to dissolve.